WASHINGTON (AP) — Attorney General Eric Holder on Thursday endorsed a proposal that would result in shorter prison sentences for many nonviolent drug traffickers, saying the change would rein in runaway federal prison costs and create a fairer criminal justice system.

Holder’s backing for a U.S. Sentencing Commission proposal to lower the guideline penalties is part of a broader Justice Department effort to lessen punishment for nonviolent drug dealers. He has been pressing to ease long mandatory sentences and has called for greater discretion for judges in sentencing.

“This focused reliance on incarceration is not just financially unsustainable — it comes with human and moral costs that are impossible to calculate,” Holder said in an appearance before the Sentencing Commission, an independent agency that establishes sentencing policies.

In a country where nearly half of all federal inmates are serving time for drug crimes, the harshest penalties should be reserved for violent drug defendants and criminals with long rap sheets, Holder said.

Holder directed prosecutors in August to stop charging many nonviolent drug defendants with offenses that carry mandatory minimum sentences. He has also said he also wants to divert people convicted of low-level offenses to drug treatment and community-service programs and to expand a prison program to allow the release of some elderly, non-violent offenders. Bipartisan legislation pending in Congress would give judges more discretion in sentencing defendants for drug crimes.

The attorney general last year asked the commission to consider reductions in the sentencing guidelines for non-violent drug crimes. The commission responded with a proposal in January that would tie many drug offenses to shorter sentencing ranges.

The effect, the Justice Department says, would be to reduce by 11 months the average sentence of a drug dealer and would trim the federal prison population by roughly 6,550 inmates at the end of the five year. The proposal would affect about 70 percent of drug trafficking offenders.

“I understand that people feel a sort of tension in this notion that we’re going to spend less, we’re going to put people in jail for smaller amounts of time, and yet you’re going to tell me that we’re going to be more safe,” Holder said in response to a question about whether the proposal could compromise public safety. “And yet, the empirical studies that I have seen, and which I have faith in, indicate that if done appropriately those are in fact the results that you can get.”

The commission was not expected to vote on the proposed change until at least April, but Holder planned to instruct prosecutors in the meantime not to oppose sentencing recommendations in line with the newly proposed ranges.

Holder’s announcement won support from groups including the American Civil Liberties, which decried what it called the “failed, racially biased war on drugs.” But a national association of prosecutors is opposing the proposal, arguing that mandatory sentences have been helpful in securing cooperation from defendants and witnesses and that the majority of federal prisoners “have been very bad actors for a long time.”

“Rewarding convicted felons with lighter sentences because America can’t balance its budget doesn’t seem fair to both victims of crime and the millions of families in America victimized every year by the scourge of drugs in America’s communities,” Raymond Morrogh, the top prosecutor in Fairfax County, Va., and the director-at-large of the National District Attorneys Association, said in prepared remarks.

Thursday was Holder’s second appearance before the Sentencing Commission.